The exhaustion of IP addresses has contributed to the development of CIDR, but the main purpose of CIDR development is to effectively use existing Internet addresses, while NAT developed according to RFC1631 (IP NETWORK ADDRESS TRANSLATOR) can be used in multiple Internet subnet The same IP address is used to reduce the use of registered IP addresses.
NAT is divided into: static NAT, dynamic NAT, port NAT (PAT).
Static NAT: Each host in the internal network is permanently mapped to a legal address in the external network;
Dynamic NAT: A series of legal addresses are defined in the external network, which is mapped to the internal network using the method of dynamic allocation;
PAT: It is a conversion method that people are more familiar with. PAT is commonly used in access equipment, it can hide small and medium-sized networks behind a legal IP address. PATT is different from dynamic address NAT. It maps internal connections to a separate IP address in the external network, and adds a TCP port number selected by the NAT device to the address. That is, the technology of port mulTIPlexing, or the technology of changing the source port of outgoing data, maps multiple internal IP addresses to the same external address.
Network Address Translation (NAT) is an Internet Engineering Task Force (IETF) standard used to allow multiple PCs on a private network (using a dedicated address segment, such as 10.0.xx, 192.168.xx, 172.xxx ) IPv4 addresses that share a single, global route. The increasing shortage of IPv4 addresses is a major reason for the frequent deployment of NAT. "Internet Connection Sharing" in Windows XP and Windows Me and many Internet gateway devices use NAT, especially when connecting to a broadband network via DSL or cable modem.
NAT is very effective for solving the problem of IPv4 address consumption (it is not necessary in IPv6 deployment), but it is a temporary solution after all. This problem of IPv4 address occupancy has become more serious in Asia and some other parts of the world, and is increasingly becoming a concern in North America. This is why people have long focused on using IPv6 to overcome this problem.
In addition to reducing the required IPv4 addresses, since all hosts outside the private network monitor communication through a shared IP address, NAT also provides a hidden layer for the private network. NAT is different from firewalls or proxy servers, but it is really good for security.
Several situations of NAT use:
1. Connect to INTERNE, but there is not enough legal address assigned to the internal host;
2. Change to an ISP that needs to reassign addresses;
3. Two INTRANETs with the same IP address are merged;
4. Want to support load balancing (host);
There are 4 usages of NAT:
1.TRANSLATION INSIDE LOCAL ADDRESS ----------- Translate the internal address one-to-one to the external address;
2. OVERLOADING INSIDE GLOBAL ADDRESS --------- Translate many-to-one internal addresses into external addresses, and distinguish different local addresses by address and port number. This method is called PAT [/ color: 43aa144927];
3.TCP LOAD DISTRIBUTING ---- Provide a method of load sharing among multiple hosts with high utilization rate;
4.HANDLING OVERLAPPING NETWORK ---- This method is mainly used for the interconnection of two INTRANET.
NAT address translation refers to the way in which each intranet address is translated into an IP address + source port, which requires multiple public IP addresses.
However, because PAT has insufficient IP addresses, the internal network address will be converted into an IP address + port segment. Such a public network IP address is usually only one.
for example:
NAT
192.168.0.2: 4444 ----> 202.116.100.5: 4444
192.168.0.3: 5555 ----> 202.116.100.6: 5555
192.168.0.10: 1233 ---> 202.116.100.5: 1233
PAT
192.168.0.2: 4444 ----> 202.116.100.5: 50003
192.168.0.3: 5555 ----> 202.116.100.5: 50004
192.168.0.10: 1233 ---> 202.116.100.5: 50005
In simple terms, PAT-many to 1, NAT-many to many.
What is Car Ethernet
Car Ethernet is a new local area network technology that uses Ethernet to connect the electronic unit in the car. Unlike traditional Ethernet, which uses 4 unshielded twisted pair cables, car Ethernet can achieve a transmission rate of 100Mbit/s or even 1Gbit/s on a single pair of unshielded twisted pair cables. At the same time, it also meets the requirements of the automotive industry for high reliability, low electromagnetic radiation, low power consumption, bandwidth allocation, low latency and synchronous real-time. The physical layer of on-board Ethernet uses BroadRReach technology, and BroadR-Reach's physical layer (PHY) technology has been standardized by the One-pair Ethernet Alliance (OPEN). Therefore, it is sometimes called Broad RReach (BRR) or OABR (Open Alliance BroadR-Reach). The MAC layer of vehicle Ethernet adopts the IEEE 802.3 interface standard and seamlessly supports widely used high-level network protocols (such as TCP/IP) without any adaptation.
On-board Ethernet protocol architecture
Vehicle-borne Ethernet and its supported upper-layer protocol architecture are shown in Figure 1. Vehicle-borne Ethernet mainly involves OSI layer 1 and Layer 2 technologies, while vehicle-borne Ethernet also supports AVB, TCP/IP, DOIP, SOME/IP and other protocols or application forms.
On-board Ethernet framework
Among them, AVB is an extension of traditional Ethernet functions, which enhances the real-time performance of traditional Ethernet audio and video transmission by adding precise clock synchronization, bandwidth reservation and other protocols, and is a network audio and video real-time transmission technology with great development potential. SOME/IP (Scalable Service-Oriented MiddlewarE on IP) specifies the video communication interface requirements for vehicle camera applications, which can be applied to the field of vehicle cameras, and realizes the mode control of driver assistance cameras through apis.
As an extension of AVB protocol, Time-Sensitive Networking (TSN) introduces related technologies of time-triggered Ethernet, which can efficiently realize the transmission of automotive control information. In addition, the on-board Ethernet of the 1Gbit communication standard also supports Power Over Ethernet (POE) function and Energy-Efficient Ethernet (EEE) function. The POE function provides power for connected terminal devices while transmitting data through twisted pair cables, eliminating the need to connect external power cables to terminals and reducing the complexity of power supply.
On-board Ethernet standardization
In terms of in-vehicle Ethernet standardization, the IEEE802.3 and IEEE802.1 working groups, AUTOSAR, the OPEN Alliance and the AVnu Alliance have played a major role in promoting it.
The IEEE802.3 local area network standard represents the mainstream Ethernet standard in the industry, and the on-board Ethernet technology is developed on the basis of IEEE802.3, so the IEEE is currently the most important international standardization body for on-board Ethernet. In order to meet the requirements of the car, it involves the development of a number of new specifications and the revision of the original specifications within the two working groups of IEEE802 and 802.1, including PHY specifications, AVB specifications, and single-wire to data line power supply. In addition, AVB related to AV transmission, timing synchronization and other specifications also need to be standardized by other technical committees of IEEE, such as IEEE1722 and IEEE1588.
OPEN Alliance
The OPEN Industry Alliance was launched in November 2011 by Broadcom, NXP, and BMW to promote the application of Ethernet-based technology standards to in-car connectivity. The main standardization goal is to develop a 100Mbit/s BroadR-R physical layer standard and develop OPEN interoperability requirements.
AUTOSAR
AUTOSAR is a consortium of automotive manufacturers, suppliers, and tool developers that aims to develop an open, standardized automotive software architecture, and the AUTOSAR specification already includes the automotive TCP/UDP/IP protocol stack.
AVnu
The AVnu Alliance was formed by Broadcom in collaboration with Cisco, Harman and Intel to promote the IEEE 802.1 AVB standard and the Time Synchronization Network (TSN) standard, establish a certification system, and address important technical and performance issues such as precise timing, real-time synchronization, bandwidth reservation, and traffic shaping.
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